1. Field of the Invention
The present invention relates to an ink for ink jet recording and an ink set for ink jet recording to be used in a recording of information containing characters, images, symbols, and the like, particularly, on plain paper copier (PPC) paper by an ink jet recording apparatus and a method for ink jet recording using the ink for ink jet recording, an ink cartridge for ink jet recording, an ink jet recording apparatus and the recorded article.
2. Description of the Related Art
The ink jet recording is known as an excellent method of recording which do not restrict the types of recording medium being used and research and studies of recording apparatuses, recording techniques, recording material for this method has been actively pursued. However, in practice, in case of ink jet recording apparatuses which have been developed and are now commercially available, when a recording medium which has been uniquely designed for ink jet recording is not used, it is difficult to obtain an image 1) having a good fixation, 2) having a so-called good xe2x80x9csharpnessxe2x80x9d in characters and free of fogging and blurring (hereinafter referred to as xe2x80x9cfeatheringxe2x80x9d), and 3) having a high image density or Optical Density (OD). When recording is performed on a recording medium, for example, paper commonly used in offices and homes such as plain paper copier paper, letter paper, bond paper, post card, writing paper, envelope, report paper, etc. and transparency films (OHP film) by a conventional ink jet recording apparatus, it is impossible to satisfy all of the properties aforementioned at the same time.
If a paper designed uniquely for ink jet recording is used, an image which exhibits aforementioned properties may be achieved. However, in general, the paper designed for ink jet recording is expensive. Also, since the paper is usually a coated paper only on its one side, fixation of ink and printing quality significantly deteriorates when recording is performed on the backside of the paper where no coating is applied. Such problem is one obstacle factor to prevent the ink jet recording apparatus to become widely used.
Therefore, various attempts to achieve the foregoing properties 1) to 3) has been pursued. For example, the following techniques have been disclosed.
(1) Strong alkaline inks exhibiting pH of around 13 as described in Japanese Patent Application Laid Open No.56-57862, Japanese Patent Application Laid Open No.57-102970 and Japanese Patent Application Laid Open No.57-102971.
(2) Method for recording which utilizes an ink ejected in a molten state, in which the molten ink is obtained by heating a solid ink in a form of wax under room temperature (for example, Japanese Patent Application Laid Open No.61-159470, Japanese Patent Application Laid Open No.62-48774 and Japanese Patent Application Laid Open No.56-57862),
(3) Method for recording which utilizes an oil-soluble ink in which a non-water-soluble organic solvent is used as a liquid medium.
Also, the following techniques are disclosed to achieve excellent fixation of the aforementioned property 1).
(4) An ink containing a large amount of surfactant, as described in Japanese Patent Application Laid Open No.55-29546.
(5) An ink comprising a combination of glycerin, N-methyl-2-pyrrolidone, a direct dye and a surfactant having a low surface tension less than cmc, as described in Japanese Patent Application Laid Open No.56-49771.
(6) Inks having a high pH and containing a fluoride surfactant, as described in Japanese Patent Application Laid Open No.56-57862 and Japanese Patent Application Laid Open No.57-102971.
The ink as aforementioned in (1) is very hazardous in handling due to the high pH. It is possible to achieve a print of excellent quality and fixation on acid paper prepared by using rosin as a sizing agent. However, ink fixation considerably deteriorates when recording on neutral papers which utilize alkyl ketene dimer or anhydride stearic acid that have recently increased production amount in Japan. Further, printing quality slightly drops. Moreover, since the strong alkaline ink can penetrate into the paper, off-setting occurs and becomes very difficult to perform two-sided printing.
The techniques as aforementioned in (2) are excellent methods satisfying the foregoing 1) to 3) properties. However, they are known to have defects that printed portions swell up, and when storing print outs by putting one upon another in a pile, the printed items can be transferred to another sheet and paper sheets can stick to each other. Also, since a separate device is required for heating the ink, the entire configuration of the recording apparatus becomes complicated.
The conventional technique as aforementioned in (3) can provide a print with excellent ink fixation. However, an offensive odor of the organic solvent contained in the ink is a troublesome matter and consideration for safety is also necessary. Therefore, they are only used for industrial application such as printing of lot numbers on the bottom of containers and outside the boxes, and rarely used in offices or at home.
The conventional technique which uses the ink aforementioned in (4) is not considered as a good technique due to the printing quality as clearly disclosed in Japanese Patent Application Laid Open No.55-80477 and Japanese Patent Application Laid Open No.56-49771.
The technique which uses the ink aforementioned in (5) has a drying rate (fixation) of 8 to 15 seconds after printing as shown in Examples. Such data clearly demonstrates that the ink is excellent in fixation as compared to the conventional art. However, when the practical situation is considered in using a recording apparatus, the time 8 to 5 seconds is found very long. Also, when holding the print outs directly after being printed out from the printing apparatus, hands of operators may be stained. In some papers, significant feathering may occur. Therefore, there are demands for improvement.
The ink of (6) is, as the present inventors confirmed, excellent ink having a fixation time of less than 5 seconds. However, it has problems with the safety, fixation and printing quality on neutral paper, off-setting, as described in the aforementioned technique (1).
In general, for use in the office or at home, aqueous inks are preferred in terms of offensive odor, safety and handling. However, when using the aqueous inks, feathering tends to occur in the portions of recording medium, where stains such as fingerprints and the like stick. Also, the printing quality may significantly change between the front and the rear of the paper. Therefore, great care is required in handling recording media when placing the recording media on an ink jet recording apparatus.
Further, as is conventionally well known, when printing by an multi-nozzle ink jet recording apparatus using an aqueous ink including 1 to 5% by weight of an aqueous dye and 20 to 50% by weight of a water-soluble organic solvent such as glycols and having a surface tension of 40 to 55 mN/m, water contained in the ink may evaporate from the nozzles. Even during the printing operation, a nozzle which are not used for printing can be clogged. For example, when printing a numeral xe2x80x9c1xe2x80x9d after repetitively printing the xe2x80x9c-xe2x80x9ds for about 120 seconds, xe2x80x9c1xe2x80x9d may not correctly be printed, since while printing xe2x80x9c-xe2x80x9ds, nozzles which are not used in printing have been clogged, and thus the ink cannot be uniformly ejected from all the nozzles.
Furthermore, when leaving the recording apparatus without printing for a while (for example, during a weekend), the viscosity of the ink is increased due to water evaporation in the ink and causes frequent ejection failure. For this reason, the apparatus should always be cleaned before using and users feel reluctant and inconvenient over this operation. Such ejection failure is more frequently observed in a recording apparatus having a weak energy used to eject the ink. Thus, in a bubble jet recording apparatus which has an ejecting energy less than ink jet apparatus using a piezo element, ejection failure occurs more frequently. Various methods to solve this problem have been considered. One of them is to install a recovery device such as a cap or pump in the recording apparatus. However, such additional components ultimately cause to raise the price of the ink jet recording apparatus.
In addition to the properties 1) to 3), the following properties are also demanded.
4) To obtain an image which do not cause blurring (color breeding) on the boundaries between different colors,
5) To obtain an image having less off-setting, to withstand two-sided printing,
6) To obtain an image having excellent durability such as water resistance, light resistance.
In order to address the demands and to improve compatibility of the ink to plain paper, aqueous inks using a pigment as a colorant has been proposed. When printing with colorant-containing aqueous ink on plain paper, an image with excellent durability can be produced. However, as for off-setting, it is still not satisfactory in two-sided printing, although it is superior to dye-containing aqueous ink. In order to use a colorant in aqueous ink as a colorant, it is important to stably disperse the colorant in an aqueous medium. Generally, colorants have poor dispersibility. Therefore, some measures are taken, in which a dispersant is added to disperse colorant in an aqueous medium, thereby forming a homogenous dispersion. However, in spite of using such dispersant, satisfying dispersion is not obtained. Furthermore, in storage over a long period of time, the dispersion is destroyed and thus, such types of aqueous ink have a problem in terms of storage stability.
Meanwhile, in order to be used in the ink jet recording, it is necessary that an ink should have properties by which it can ejected in stable liquid droplets from micro ends of an ink jet recording head. Also, the ink should not be solidified by dehydration of an orifice of the ink jet recording head. However, when using ink containing a dispersant, resins forming the dispersant may be bonded to parts of the ink jet recording head such as orifices. If the resins are not redissolved, problems such as clogging of the recording head and ejection failure may be caused. Especially, when the recording head is not used for a long period of time, the head tends to be clogged easily. Also, the ink may accumulate in supporting devices such as a nozzle cap or sucking tube, possibly causing damage to their functions. When the printing is once intermitted, or a nozzle corresponding to blank spaces of a document or image does not perform printing for a while, the ejecting direction of ink droplets may be scattered. So-called bad printing (intermittent ejection failure) may occur. Moreover, the aqueous colorant ink containing a dispersant is typically viscose and dense. Therefore, in case of a continuous printing or a high-speed printing, the ink may encounter a resistance on its way to a nozzle end. As a result, ejection becomes unstable and the printing cannot be performed smoothly.
Regarding the above mentioned problems, many techniques have been proposed. For example, Japanese Patent Application Laid Open No.5-186704 and Japanese Patent Application Laid Open No.8-3498 disclose black inks containing a self-dispersible carbon black, in which the carbon black has a hydrophilic group introduced on its surface, and allows stable dispersion without a dispersant. Japanese Patent Application No. 2000-513396 disclosed color inks containing colorants which can be stably dispersed without a dispersant.
However, the ink of Japanese Patent Application No.2000-513396 does not provide solution to the intermittent ejection failure. Therefore, the conventional color colorant inks, including the self-dispersible colorant ink cannot provide colorant content sufficient for high quality image. Also, even when combined with an ink composition having a penetration rate sufficiently high for use in the high-speed printing on plain paper an image with good color tone and image density cannot be obtained.
Thus, an object of the present invention is to provide an excellent ink for ink jet recording, ink set for ink jet recording, a method for ink jet recording, an ink jet recording apparatus and an ink cartridge, and recorded article for which 1) the recording medium is not restricted, that is, not affected by the surface properties, materials and construction of the paper, film, and the like; 2) a high image density (OD) can be obtained; 3) high quality print outs can be obtained without hardly causing feathering; 4) exhibit excellent fixation of an ink; and 5) accurate print outs highly reliable may be obtained at any time without a support of complex recovery device.
Another object of the present invention is to provide an excellent ink for ink jet recording, ink set for ink jet recording, a method for ink jet recording, an ink jet recording apparatus and an ink cartridge, characterized by the following properties: 1) excellent ejection stability when printed under high speed on plain paper particularly by a method for ink jet recording and which renders excellent storage stability; 2) good color tone; 3) high image density; 4) an accurate and clear image without causing fogging or blurring (hereinafter referred to as xe2x80x9cfeatheringxe2x80x9d) at peripheral of the characters or images; 5) causing much less blurring (color breeding) on the interfaces between different colors; 6) less off-setting, thereby allowing two-sided printing; and 7) durability of the produced image in terms of water resistance, resistance to light, and the like.
Yet another object of the present invention is to provide a stable ink for ink jet recording, a method for ink jet recording, an ink jet recording apparatus and an ink cartridge, which perform smooth and natural reproduction of complicated Chinese characters, slant lines or curves.
Yet another object of the present invention is to provide an ink for ink jet recording, ink set for ink jet recording, a method for ink jet recording, an ink jet recording apparatus and an ink cartridge, which allows printing of an image having excellent water resistance.